In ClickHouse, the JOIN reflex is wrong about 80% of the time. dictGet runs 20× faster than the equivalent JOIN on a 10-billion-row enrichment. When dictionaries win, when JOINs still beat them, and how to skip the lookup entirely by enriching at ingest.
The complete ClickHouse query optimization guide: sorting keys, PREWHERE, data skipping indexes, FINAL evolution, JOIN algorithms, the diagnostic toolkit, and the anti-patterns that quietly undo everything else.
ClickHouse projections explained: internal storage, query routing, three projection types, and a decision framework for when to use them vs materialized views.
CollapsingMergeTree trades ingestion complexity for query simplicity. Cancel the old row, insert the new one — merges do the rest. No FINAL, no argMax, just sum(col * Sign).
Building cascading AggregatingMergeTree tables for real-time OHLC candles served through TradingView's UDF API, with live streaming via Durable Objects.
I'm always working on new ideas. Check back regularly for updates.
